iOS 10 beta NSURLSession request's cookie is gone

I have an APP which use NSURLSession to connect the server to retrieve data. In iOS 9, it works well. Just recently iOS is about to be released and I upgrade Xcode and use iOS 10 Beta SDK... it turns out the HTTP GET request didn't contain the Cookie session information. That makes the request fail. I have searched here for iOS 10 beta's problems about cookie but not much luck. Would like to ask anyone had experienced this and any advice??? Thank you in advance.